This project is to determine the kinematics of adult knee joints and post-arthroplasty joint replacements using a system of three-dimensional radiographic analysis of in-vivo bony structures. Implanted markers will be utilized to determine the kinematics of both normal and pre-arthroplasty deranged knees. The normative data will be for adults of both sexes and varying ages. The resultant post-arthroplasty kinematics of constrained, semi-constrained and totally constrained prosthetic types will be determined. The sensitivity of this analysis technique to detect joint loosening will be evaluated.